Soil erosion is the wearing of and displacement of a field’s topsoil by natural or physical forces like water, animals, or wind. It involves the detachment of the soil, its movement, and deposition. Soil erosion can be accelerated by the following degradation conditions: compaction, low organic matter, poor internal drainage, salinization soil acidity, and loss of soil structure. Soil erosion can be a slow and unnoticed process or the process can also be at an alarming rate resulting in serious damage to the top soil. Erosion mostly results in the loss of soil from the farmland leading to reduced crop production potential, lower surface water quality, and damaged drainage networks. The availability of nitrogen in the soil is in different forms and it constantly changes from one form to another. These forms of nitrogen in the soil follow paths through the ecosystem and are collectively called the nitrogen cycle. Nitrogen nutrient composition in the soil is available in both inorganic and organic forms. Organic nitrogen is composed of amides (NH2) and makes more than 90% of total nitrogen in most environments (Espinoza, 2013). These nutrients are found in organic matter called humus; an easily decomposed material, soil microbes, and some other organic molecules. Inorganic nitrogen, on the other hand, is the conversion of nitrogen that is present in soil organic matter, crop residues, and manures to the inorganic form by the process of mineralization (Espinoza, 2013). The process transforms organic nitrogen into ammonia (NH3) and ammonium (NH4 +) forms in a process called ammonification (Espinoza, 2013). The ammonium state obtained is then transformed into the nitrate form by a process called nitrification. The availability of phosphorus (P) in soils is in both organic and inorganic forms. In either form, phosphorus availability in the soil solution is in very low amounts or associated with soil minerals or organic materials. The amounts of each form vary in different soils and that of clayey-textured is 10 times greater than that in sandy soil (Espinoza, 2013). Organic phosphorous in the soil is made up of microbial compounds. Since organic P is not directly available for plant uptake the organic materials are decomposed by microbes in the soil and phosphorous is released in a process called mineralization. The mineralization rate is affected by soil moisture, the composition of the organic material, oxygen concentration, and pH. Inorganic P in soil solution at any given time is very small and amounts to less than 1 lb/A (Espinoza, 2013). Inorganic P in the soil occurs mostly as aluminum, iron, or calcium compounds. Water in this case is the physical force behind the detachment of the soil, its movement, and deposition. The rate and magnitude of soil erosion in this case are controlled by, rainfall and runoff, Soil erodibility, slope gradient and length, cropping and vegetation, and lastly tillage practices (Balasubramanian, 2017). In rainfall and runoff factors the greater the intensity and duration of a rainstorm, the higher the erosion potential. The impact of raindrops breaks down and disperses soil aggregates which are washed by runoff water. In soil erodibility, erosion depends on the susceptibility of soil to the agent of erosion. The soil's physical characteristics such as texture, structure, soil organic matter content, and clay minerals would determine its ability to resist erosion (Balasubramanian, 2017). In slope gradient and length the steeper and longer the slope of a field, the higher the risk for erosion due to greater accumulation of runoff. In cropping and vegetation erosion increases with a decrease in vegetative cover of plants or crops which protects the soil from raindrop impact and splash. Furthermore, they slow down the movement of runoff. Lastly, when tillage is up or down the slopes, water runoff is increased accelerating the soil erosion process. In this case, the wind is the physical force behind the detachment of the soil, its movement, and deposition. It happens when an airstream passes over a surface with sufficient lift and drag to overcome the forces of gravity, friction, and cohesion (Balasubramanian, 2017). The impact of the force of the wind dislodges the particles from the surface and transports them in suspension, saltation, or by surface creep. The rate and magnitude of erosion in this case are controlled by soil surface roughness, climate, unsheltered distance, topography, and cultural practices (Balasubramanian, 2017). In soil surface roughness, smoother surfaces offer less resistance, and the soil is easily blown by the wind. The effect of climate on erosion is in climate change. For example in the drought season, moisture levels in the ground are low making the soil particles lose and easily blown. In the case of unsheltered distances the lack of windbreakers such as trees and shrubs, the wind is eroded for longer distances. Due to the increasing human population, there is a need to develop farmlands to accommodate the growing population. The construction activities result in the production of much sediment on the surface due to vigorous activities. In addition, the vegetative cover of the plants is destroyed when the trees are cut off to allow room for construction. Since the potential for erosion on highly disturbed land is commonly 100 times greater than on agricultural land (Staff, 2013) the exposed ground is more susceptible to erosion. Erosion in urban areas leads to loss of nutrients and nutrient holding capacity of the soil resulting in less fertile soil for landscape plants. Sediment reduces water quality by making the water turbid reducing the penetration of light to the underwater plants. Turbidity also reduces oxygen levels in the water degrading aquatic life. When sediments build up in the stream it reduces its flow capacity which results in flooding. The erosion-reducing effectiveness of plants depends on the extent and quantity of cover (Balasubramanian, 2017). Soil erosion is greater in an area with no or very little vegetative cover of plants than in a place covered with plants. A ground with plant cover is protected from raindrop impact and splash reducing the soil's ability to erode . In addition, runoff water is also slower in a place covered with plants allowing it enough time to infiltrate. Plant roots hold the soil in position and prevent it from being blown or washed away. Plants play an important role in wetlands and on the river banks as they slow the flow of the water and their roots bind the soil. Erosion can be managed by a number of factors including temporary and permanent vegetation, mulching, rolled erosion control products (RECPs), PAM application for erosion control, and outlet protection (Staff, 2013). In temporary and permanent vegetation during construction, temporary plants are grown during to prevent runoffs and erosion. Mulching limits soil erosion and lessens the need to contain sediment as it ensures residue remains in place. It also protects the soil surface from the impact of raindrops and erosive forces of wind until the vegetative cover is established. RECP is achieved by applying Turf Reinforcement Mats of organic or synthetic materials to the soil surface protecting it from erosion until the vegetative cover is established. PAM application for erosion control is achieved by applying products containing water-soluble anionic polyacrylamide (PAM) as temporary soil-binding agents to reduce erosion. Land owners' decisions on conservation practices differ in regard to the approach. The different approaches are: adopting expensive conservation practices such as terraces and drainage tile, adopting inexpensive conservation practices in the grassed waterway and seeded downstream banks, adopting conservation tillage such as mulch, reduced and no-till, and finally having land enrolled in conservation programs (Duffy & Calvert, 2012). Land owners' decision to adopt inexpensive cultivation practices is for holding land to earn income. Due to the recurring cost of farming when adopting inexpensive practices land owners opt for expensive ones. Expensive practices have effects that last over long periods of time hence they are cost-effective to landlords.
References
Duffy, M., & Calvert, L. (2012). Conservation practices for landlords.
Espinoza, L. (2013). The Nitrogen and Phosphorous Cycle in Soils. University of Arkansas, United States Department of Agriculture and County Governments Cooperating. FSA2148-2M-10-05N. Printed by University of Arkansas Cooperative Extension Service Printing Services.
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Staff, W. C. C. (2013). Natural Resources Conservation Service, United States Department of Agriculture. SCAN Database for Walnut Gulch Station, 2026.
Balasubramanian, A. (2017). Soil Erosion – Causes and Effects. Retrieved on 13 July 2018. From file:///C:/Users/f/Downloads/SoilErosionCausesandEffects.pdf.
